An activation method for proton exchange membrane fuel cell stacks based on AC impedance meter

Abstract

This invention relates to an activation method for a proton exchange membrane fuel cell stack based on an AC impedance meter. The steps include: checking the airtightness of the stack; heating the stack and purging the anode and cathode with nitrogen gas; introducing hydrogen gas into the anode and nitrogen gas into the cathode, with the anode pressure greater than the cathode pressure; switching the nitrogen gas at the cathode to air; performing oxygen-deficient activation; performing constant current discharge activation and recording polarization curve 1; repeating oxygen-deficient activation and constant current discharge activation to obtain multiple polarization curves; determining whether the impedance deviation of a single cell between the new polarization curve and the previous polarization curve is less than 0.2 mΩ; if so, further determining whether the voltage deviation between the new polarization curve and the previous polarization curve is less than 10 mV, thus completing the stack activation. This invention rapidly reduces oxides on the catalyst surface, improving catalyst activity and utilization, fully wetting the proton exchange membrane, establishing good ion channels, accelerating stack activation, and reducing hydrogen consumption.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to an activation method for a proton exchange membrane fuel cell stack based on an AC impedance meter. Background Technology

[0002] Following the rapid development of new energy sources such as solar and wind power, hydrogen energy, recognized as a low-carbon and zero-carbon energy source, is emerging as a rising star. The sustained high popularity of hydrogen energy is not without reason. As a clean energy source, it possesses characteristics such as high compression ratio, large-scale storage, and no energy decay. Its sources are widespread and its applications are extensive, effectively reducing the proportion of fossil fuels and improving the level of clean development. Developing hydrogen energy is an important vehicle for building a "multi-energy complementary" energy supply system and a significant contributor to achieving energy transformation and upgrading.

[0003] Therefore, people are paying increasing attention to environmentally friendly and highly efficient fuel cell vehicles to replace polluting internal combustion engine vehicles. Among these, the proton exchange membrane fuel cell is the core component of a fuel cell vehicle. It is an electrochemical device that directly converts the chemical energy of hydrogen into electrical energy, heat energy, and water through a reaction. Its characteristics include zero pollution, with emissions consisting only of water; and high energy efficiency. As long as there is sufficient fuel gas (hydrogen and oxygen), it can operate continuously for extended periods.

[0004] A fuel cell stack consists of hundreds of individual cells. Each cell includes a membrane electrode assembly (MEA) and bipolar plates on both sides. The MEA comprises a gas diffusion layer, a catalyst layer, and a proton exchange membrane.

[0005] After the fuel cell stack is assembled, it cannot be used directly, as its initial performance is relatively low. Therefore, it must be activated before use to maximize its initial performance. Fuel cell activation involves: thoroughly wetting the proton exchange membrane with water to ensure hydrogen ion channels; removing impurities from the polymer electrolyte membrane or electrodes to improve ionic conductivity; reducing platinum oxide to enhance catalytic activity; and establishing a good three-phase reaction interface, allowing the fuel cell stack to achieve its optimal operating state and performance.

[0006] Currently, the common method for rapid activation of fuel cell stacks is to pre-activate them by introducing humidified nitrogen gas, followed by subjecting the stack to high current for an extended period. However, this method has drawbacks: it requires a long activation time and consumes a large amount of hydrogen, which hinders the mass production of fuel cell stacks. Therefore, an activation process is needed that can accelerate the activation time of fuel cell stacks while reducing the amount of hydrogen used, thus preparing for the mass production of fuel cell vehicles.

[0007] Chinese patent CN202210004379.8 discloses an anode activation method for a proton exchange membrane fuel cell stack. The steps include: detecting the stack's airtightness; heating the stack and purging the anode and cathode with nitrogen gas; introducing hydrogen gas into the anode and nitrogen gas into the cathode, with the anode pressure greater than the cathode pressure; applying voltage to individual cells; switching the nitrogen gas at the cathode to air; applying voltage to individual cells and decreasing the voltage according to a fixed voltage value; repeatedly applying voltage to individual cells, obtaining multiple polarization curves, and determining whether the voltage deviation between the new polarization curve and the previous polarization curve is less than 10mV, thus completing the stack activation. This patent reduces oxides on the catalyst surface, improving catalyst activity and utilization. However, a drawback of this patent is that while pre-activation is added to wet the membrane, constant current activation is still used, resulting in a less significant acceleration effect. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the existing technology by providing an activation method for proton exchange membrane fuel cell stacks based on an AC impedance meter. By using an AC impedance meter to determine the impedance of the proton exchange membrane, appropriate activation methods can be adopted, resulting in more effective activation. This significantly shortens the activation time of the fuel cell stack and reduces hydrogen consumption. By using more advanced equipment, the state of the membrane electrode assembly (MEA) can be better determined, and different activation methods can be adopted for different MEA states. Therefore, using an AC impedance meter during activation can effectively determine the impedance of the membrane in the MEA, showing the degree of wetting of the proton exchange membrane, and different activation methods can be adopted according to this state to quickly complete the stack activation.

[0009] The objective of this invention can be achieved through the following technical solutions:

[0010] An activation method for a proton exchange membrane fuel cell stack based on an AC impedance meter, comprising the following specific steps:

[0011] Step N1: Place the proton exchange membrane fuel cell on the test platform, connect the gas pipeline, and check the stack's airtightness.

[0012] Step N2: Set the fuel cell temperature to temperature 1, introduce humidified nitrogen gas into the cathode, and introduce humidified hydrogen gas into the anode. At this time, the humidity of the anode and cathode is humidity 1 and humidity 2, respectively. The cathode flow rate is flow rate 1, the anode flow rate is flow rate 2, and the back pressure of the anode and cathode is pressure 1 and pressure 2, respectively.

[0013] Step N3: The fuel cell stack temperature reaches temperature 1. After the fuel cell stack temperature is maintained at temperature 1 for a time T1, the fuel cell stack pre-activation process ends, and the fuel cell stack temperature is set to temperature 2.

[0014] Step N4: After the stack temperature reaches stack temperature 2 and stabilizes, nitrogen gas is stopped flowing into the cathode, the anode and cathode flow control is set to metering ratio mode, humidifying air is introduced, the minimum flow rate of the cathode is flow rate 3, the cathode metering ratio is metering ratio 1, the cathode humidity is humidity 3, the minimum flow rate of the anode is flow rate 4, the anode metering ratio is metering ratio 2, the anode humidity is humidity 4, and the anode and cathode back pressures are pressure 3 and pressure 4, respectively.

[0015] Step N5, under-oxygen activation: Load the fuel cell stack to voltage 1, then stop the air supply to the cathode, the stack voltage drops to voltage 2, air is supplied again, the load is disconnected, the voltage recovers to OCV, repeat this step K1 times.

[0016] Step N6, Constant Current Discharge Activation: Start applying 0.5V from OCV at a rate of 0.2 A / cm. 2 0.2 A / cm 2 Hold for 3-5 minutes, at a rate of 0.2 A / cm. 2 The value of the last point is taken to form polarization curve 1, where the horizontal axis of polarization curve 1 is current density and the vertical axis is average voltage.

[0017] Step N7: Repeat steps N5 and N6 to obtain polarization curve 2. The horizontal axis of polarization curve 2 is the current density, and the vertical axis is the average voltage. Use an AC impedance meter to measure the impedance value and determine whether the deviation of the average single-piece impedance of the two polarization curves is less than 0.2mΩ. If it is greater than 0.2mΩ, repeat steps N5, N6, and N7; if it is less than 0.2mΩ, proceed to step N8.

[0018] Step N8: Determine whether the voltage deviation between polarization curve 2 and polarization curve 1 is less than 10mV within the voltage range of 0.55V to 0.75V and under the same current. If yes, the stack has been activated. If the voltage deviation between polarization curve 2 and polarization curve 1 is greater than or equal to 10mV, repeat step N8 until the voltage deviation between the new polarization curve and the previous polarization curve is less than 10mV, and the stack activation is complete.

[0019] Furthermore, before step N1, there is also step N0, which detects whether the airtightness of the fuel cell stack meets the airtightness index. If it meets the airtightness index, the process proceeds to step N1. If it does not meet the airtightness index, the fuel cell stack is reassembled until the airtightness of the fuel cell stack meets the airtightness index.

[0020] Further, in step N2, the formula for calculating the flow rate 1 is: 0.00696 * effective area * current density * number of single cells * metering ratio;

[0021] The formula for calculating the flow rate 2 is: 0.01657 * effective area * current density * number of single cells * metering ratio.

[0022] The stack comprises several individual cells, the effective area is the area of ​​a single cell, the current density is the input value of the external device of the stack, and the metering ratio ranges from 1 to 3.

[0023] Furthermore, in step N2, pressure 1 and pressure 2 are atmospheric pressure, wherein pressure 1 and pressure 2 are both gauge pressures.

[0024] Furthermore, in step N2, the temperature 1 of the fuel cell stack is 60°C.

[0025] Furthermore, in step N2, the relative humidity value of humidity 1 = humidity 2 = relative humidity is 100%.

[0026] Furthermore, in step N3, the specific method for setting the stack temperature to reach temperature 1 is as follows: the coolant is preheated to temperature 1 and maintained at temperature 1, and the coolant at the first temperature value is introduced into the stack for heating treatment.

[0027] Furthermore, in step N3, T1 is 1-5 minutes.

[0028] Furthermore, in step N3, the temperature 2 of the fuel cell stack is 70°C.

[0029] Further, in step N4, the formula for calculating the flow rate 3 is: 0.00696 * effective area * current density * number of single cells * metering ratio;

[0030] The formula for calculating the flow rate 4 is: 0.01657 * effective area * current density * number of single cells * metering ratio.

[0031] The stack comprises several individual cells, the effective area is the area of ​​a single cell, the current density is the input value of the external device of the stack, and the metering ratio ranges from 1 to 3.

[0032] Furthermore, flow rate 1 is equal to flow rate 3, and flow rate 2 is equal to flow rate 4.

[0033] Further, in step N4, the pressure 3 is 100kPa to 150kPa, and the pressure 4 is 100kPa to 150kPa. Both pressure 3 and 4 are gauge pressures, and pressure 4 is 10-20kPa higher than pressure 3.

[0034] Furthermore, in step N4, the relative humidity value is 60%.

[0035] Furthermore, in step N5, voltage 1 is 0.8 V and voltage 2 is 0.3 V.

[0036] Furthermore, in step N5, K1 is 5-10 times.

[0037] Further, in step N6, the polarization curve is obtained by a linear scanning method, wherein the scanning range of the linear scanning method is OCV-0.5V, the scanning speed is 5mV / s, and OCV is the open circuit voltage.

[0038] Furthermore, in step N7, the average impedance of a single cell is equal to the total impedance value measured by the AC impedance meter divided by the number of single cells in the stack.

[0039] Compared with the prior art, the advantages of the present invention are as follows:

[0040] 1. This invention improves the activity and utilization rate of the catalyst by reducing the oxides on the surface of the catalyst;

[0041] 2. This invention fully wets the proton exchange membrane, constructs an efficient and stable three-phase reaction interface and a good gas-liquid transport channel inside the membrane electrode, and removes impurities from the polymer electrolyte membrane or electrode to improve ionic conductivity;

[0042] 3. Compared with the traditional constant current activation method of high current forced discharge, this invention uses an AC impedance meter to determine the impedance of the proton exchange membrane and adopts corresponding activation methods, which is more effective in activating the fuel cell stack, greatly shortening the activation time and reducing the amount of hydrogen used. Attached Figure Description

[0043] Figure 1 This is a flowchart of the activation method for a proton exchange membrane fuel cell stack based on an AC impedance meter according to the present invention.

[0044] Figure 2 This is a schematic diagram of an activation cycle in steps N5 and N6 of the present invention;

[0045] Figure 3 A comparison diagram of polarization curves obtained for the example;

[0046] Figure 4 This is a comparison chart of polarization curves obtained for comparison. Detailed Implementation

[0047] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0048] An activation method for a proton exchange membrane fuel cell stack based on an AC impedance meter, comprising the following specific steps:

[0049] Step N1: Place the proton exchange membrane fuel cell on the test platform, connect the gas pipeline, and check the stack's airtightness.

[0050] Step N2: Set the fuel cell temperature to temperature 1, introduce humidified nitrogen gas into the cathode, and introduce humidified hydrogen gas into the anode. At this time, the humidity of the anode and cathode is humidity 1 and humidity 2, respectively. The cathode flow rate is flow rate 1, the anode flow rate is flow rate 2, and the back pressure of the anode and cathode is pressure 1 and pressure 2, respectively.

[0051] Step N3: The fuel cell stack temperature reaches temperature 1. After the fuel cell stack temperature is maintained at temperature 1 for a time T1, the fuel cell stack pre-activation process ends, and the fuel cell stack temperature is set to temperature 2.

[0052] Step N4: After the stack temperature reaches stack temperature 2 and stabilizes, nitrogen gas is stopped flowing into the cathode, the anode and cathode flow control is set to metering ratio mode, humidifying air is introduced, the minimum flow rate of the cathode is flow rate 3, the cathode metering ratio is metering ratio 1, the cathode humidity is humidity 3, the minimum flow rate of the anode is flow rate 4, the anode metering ratio is metering ratio 2, the anode humidity is humidity 4, and the anode and cathode back pressures are pressure 3 and pressure 4, respectively.

[0053] Step N5, under-oxygen activation: Load the fuel cell stack to voltage 1, then stop the air supply to the cathode, the stack voltage drops to voltage 2, air is supplied again, the load is disconnected, the voltage recovers to OCV, repeat this step K1 times.

[0054] Step N6, Constant Current Discharge Activation: Start applying 0.5V from OCV at a rate of 0.2 A / cm. 2 0.2 A / cm 2 Hold for 3-5 minutes, at a rate of 0.2 A / cm. 2 The value of the last point is taken to form polarization curve 1, where the horizontal axis of polarization curve 1 is current density and the vertical axis is average voltage.

[0055] Step N7: Repeat steps N5 and N6 to obtain polarization curve 2. The horizontal axis of polarization curve 2 is the current density, and the vertical axis is the average voltage. Use an AC impedance meter to measure the impedance value and determine whether the deviation of the average single-piece impedance of the two polarization curves is less than 0.2mΩ. If it is greater than 0.2mΩ, repeat steps N5, N6, and N7; if it is less than 0.2mΩ, proceed to step N8.

[0056] Step N8: Determine whether the voltage deviation between polarization curve 2 and polarization curve 1 is less than 10mV within the voltage range of 0.55V to 0.75V and under the same current. If yes, the stack has been activated. If the voltage deviation between polarization curve 2 and polarization curve 1 is greater than or equal to 10mV, repeat step N8 until the voltage deviation between the new polarization curve and the previous polarization curve is less than 10mV, and the stack activation is complete.

[0057] Furthermore, before step N1, there is also step N0, which detects whether the airtightness of the fuel cell stack meets the airtightness index. If it meets the airtightness index, the process proceeds to step N1. If it does not meet the airtightness index, the fuel cell stack is reassembled until the airtightness of the fuel cell stack meets the airtightness index.

[0058] Further, in step N2, the formula for calculating the flow rate 1 is: 0.00696 * effective area * current density * number of single cells * metering ratio;

[0059] The formula for calculating the flow rate 2 is: 0.01657 * effective area * current density * number of single cells * metering ratio.

[0060] The stack comprises several individual cells, the effective area is the area of ​​a single cell, the current density is the input value of the external device of the stack, and the metering ratio ranges from 1 to 3.

[0061] Furthermore, in step N2, pressure 1 and pressure 2 are atmospheric pressure, wherein pressure 1 and pressure 2 are both gauge pressures.

[0062] Furthermore, in step N2, the temperature 1 of the fuel cell stack is 60°C.

[0063] Furthermore, in step N2, the relative humidity value of humidity 1 = humidity 2 = relative humidity is 100%.

[0064] Furthermore, in step N3, the specific method for setting the stack temperature to reach temperature 1 is as follows: the coolant is preheated to temperature 1 and maintained at temperature 1, and the coolant at the first temperature value is introduced into the stack for heating treatment.

[0065] Furthermore, in step N3, T1 is 1-5 minutes.

[0066] Furthermore, in step N3, the temperature 2 of the fuel cell stack is 70°C.

[0067] Further, in step N4, the formula for calculating the flow rate 3 is: 0.00696 * effective area * current density * number of single cells * metering ratio;

[0068] The formula for calculating the flow rate 4 is: 0.01657 * effective area * current density * number of single cells * metering ratio.

[0069] The stack comprises several individual cells, the effective area is the area of ​​a single cell, the current density is the input value of the external device of the stack, and the metering ratio ranges from 1 to 3.

[0070] Furthermore, flow rate 1 is equal to flow rate 3, and flow rate 2 is equal to flow rate 4.

[0071] Further, in step N4, the pressure 3 is 100kPa to 150kPa, and the pressure 4 is 100kPa to 150kPa. Both pressure 3 and 4 are gauge pressures, and pressure 4 is 10-20kPa higher than pressure 3.

[0072] Furthermore, in step N4, the relative humidity value is 60%.

[0073] Furthermore, in step N5, voltage 1 is 0.8 V and voltage 2 is 0.3 V.

[0074] Furthermore, in step N5, K1 is 5-10 times.

[0075] Further, in step N6, the polarization curve is obtained by a linear scanning method, wherein the scanning range of the linear scanning method is OCV-0.5V, the scanning speed is 5mV / s, and OCV is the open circuit voltage.

[0076] Furthermore, in step N7, the average impedance of a single cell is equal to the total impedance value measured by the AC impedance meter divided by the number of single cells in the stack.

[0077] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0078] Example

[0079] refer to Figures 1 to 3 This embodiment provides an activation method for a proton exchange membrane fuel cell stack based on an AC impedance meter, comprising the following steps:

[0080] The test sample in this implementation was: one piece with an effective area of ​​25 cm². 2 The stack of membrane electrodes is activated.

[0081] Step N0: Check whether the airtightness of the fuel cell stack meets the airtightness index. If it meets the airtightness index, proceed to step N1. If it does not meet the airtightness index, reassemble the fuel cell stack until the airtightness of the fuel cell stack meets the airtightness index.

[0082] Step N1: Place the proton exchange membrane fuel cell on the test platform, connect the gas pipeline, and check the stack's airtightness.

[0083] Step N2: Set the fuel cell temperature to 60℃. Introduce humidified nitrogen gas to the cathode and humidified hydrogen gas to the anode. Purge both the anode and cathode with nitrogen gas for 20 seconds. At this point, the humidity at both the anode and cathode is 100%. The gas pressure at both the anode and cathode is atmospheric pressure. The cathode flow rate is Flow Rate 1, and the cathode nitrogen purging flow rate 1 is 0.5 A / cm³, which is normal for the fuel cell stack. 2The gas flow rate is: 0.01657 * 25 * 0.5 * 2.5 = 0.518 L / min. The anode flow rate is flow rate 2, and the anode hydrogen purging flow rate 2 is 0.5 A / cm³ during normal operation of the fuel cell stack. 2 The gas flow rate is: 0.00696 * 25 * 0.5 * 1.8 = 0.157 L / min;

[0084] Step N3: The fuel cell stack temperature reaches 60°C and is maintained at 60°C for 5 minutes. The fuel cell stack pre-activation process is completed, and the fuel cell stack temperature is set to 70°C.

[0085] Step N4: After the fuel cell stack temperature reaches 70℃ and stabilizes, stop supplying nitrogen to the cathode. Set the anode and cathode flow control to metering ratio mode and introduce humidified air. The minimum flow rate at the cathode is 0.518 L / min, the metering ratio is 2.5, the gas pressure is 90 kPa, and the humidity is 60%. The minimum flow rate at the anode is 0.157 L / min, the metering ratio is 1.8, the gas pressure is 100 kPa, and the humidity is 60%.

[0086] Step N5, under-oxygen activation: Load the fuel cell stack to a voltage of 0.8V, then stop the air supply to the cathode. The stack voltage drops to 0.3V. Resume the air supply, disconnect the load, and the voltage returns to OCV. Repeat this step 5 times.

[0087] Step N6, Constant Current Discharge Activation: Start applying 0.5V from OCV at a rate of 0.2 A / cm. 2 0.2 A / cm 2 Hold for 3-5 minutes, at a rate of 0.2 A / cm. 2 The value of the last point is used to form polarization curve 1.

[0088] Step N7: Repeat steps N5 and N6 to obtain polarization curve 2. Use an AC impedance meter to measure the impedance value and determine whether the deviation of the average single-cell impedance of the two impedance curves (the average single-cell impedance is equal to the total impedance value measured by the AC impedance meter / the number of single cells in the stack) is less than 0.2mΩ. If it is greater than 0.2mΩ, repeat steps N5, N6, and N7. If it is less than 0.2mΩ, proceed to step N8.

[0089] Step N8: Determine whether the voltage deviation between polarization curve 2 and polarization curve 1 is less than 10mV under the same voltage of 0.4V and 0.6V and the same current. If so, the stack has been activated. If the voltage deviation between polarization curve 2 and polarization curve 1 is greater than or equal to 10mV, repeat step N8 until the voltage deviation between the new polarization curve and the previous polarization curve is less than 10mV, and the stack activation is complete.

[0090] like Figure 3The figure shown is a comparison of the polarization curves obtained in this embodiment.

[0091] like Figure 3 As shown, this activation process involved five activation cycles. Polarization curve 1 represents the polarization curve obtained after one activation cycle, while polarization curves 2 and 3 represent the polarization curves obtained after the last two cycles. During the first three activation cycles, the deviation of the average single-cell impedance of the two impedance curves was greater than 0.2 mΩ, and under-energization was performed in all of them. In the fourth activation cycle, the deviation of the average single-cell impedance was less than 0.2 mΩ, but the voltage deviation was greater than 10 mV compared to the previous cycle, so a fifth activation cycle was performed. The impedance deviation of the fifth activation cycle compared to the fourth activation cycle was less than 0.2 mΩ, and the voltage deviation was less than 10 mV. The stack activation was completed. The total activation time was 150 minutes.

[0092] This embodiment uses an AC impedance meter to determine the impedance of the proton exchange membrane and adopts corresponding activation methods to activate it more effectively, greatly shortening the activation time of the fuel cell stack and reducing the amount of hydrogen used.

[0093] Comparative Example

[0094] This comparative example uses a conventional activation method, specifically a conventional constant current activation. The comparative example includes the following steps:

[0095] The test sample in this implementation was: one piece with an effective area of ​​25 cm². 2 The stack of membrane electrodes is activated.

[0096] Step N0: Check whether the airtightness of the fuel cell stack meets the airtightness index. If it meets the airtightness index, proceed to step N1. If it does not meet the airtightness index, reassemble the fuel cell stack until the airtightness of the fuel cell stack meets the airtightness index.

[0097] Step N1: Place the proton exchange membrane fuel cell on the test platform, connect the gas pipeline, and check the stack's airtightness.

[0098] Step N2: Set the fuel cell temperature to 60℃. Introduce humidified nitrogen gas to the cathode and humidified hydrogen gas to the anode. Purge both the anode and cathode with nitrogen gas for 20 seconds. At this point, the humidity at both the anode and cathode is 100%. The gas pressure at both the anode and cathode is atmospheric pressure. The cathode flow rate is Flow Rate 1, and the cathode nitrogen purging flow rate 1 is 0.5 A / cm³, which is normal for the fuel cell stack. 2 The gas flow rate is: 0.01657 * 25 * 0.5 * 2.5 = 0.518 L / min. The anode flow rate is flow rate 2, and the anode hydrogen purging flow rate 2 is 0.5 A / cm³ during normal operation of the fuel cell stack. 2 The gas flow rate is: 0.00696 * 25 * 0.5 * 1.8 = 0.157 L / min;

[0099] Step N3: The fuel cell stack temperature reaches 60°C and is maintained at 60°C for 5 minutes. The fuel cell stack pre-activation process is completed, and the fuel cell stack temperature is set to 70°C.

[0100] Step N4: After the fuel cell stack temperature reaches 70℃ and stabilizes, stop supplying nitrogen to the cathode. Set the anode and cathode flow control to metering ratio mode and introduce humidified air. The minimum flow rate at the cathode is 0.518 L / min, the metering ratio is 2.5, the gas pressure is 90 kPa, and the humidity is 60%. The minimum flow rate at the anode is 0.157 L / min, the metering ratio is 1.8, the gas pressure is 100 kPa, and the humidity is 60%.

[0101] Step N5, Constant Current Discharge Activation: Start applying 0.5V from OCV at a rate of 0.2 A / cm. 2 0.2 A / cm 2 Hold for 3-5 minutes, at a rate of 0.2 A / cm. 2 The value of the last point is used to form polarization curve 1.

[0102] Step N6: Repeat step N5 to obtain polarization curve 2. Under the same current, check if the voltage deviation between polarization curve 2 and polarization curve 1 is less than 10mV. If so, the stack has been activated. If the voltage deviation between polarization curve 2 and polarization curve 1 is greater than or equal to 10mV, repeat step N6 until the voltage deviation between the new polarization curve and the previous polarization curve is less than 10mV, thus completing the activation of the stack.

[0103] like Figure 4 The figure shown is a comparison of the polarization curves obtained in this embodiment.

[0104] like Figure 4 As shown, this activation process consisted of 7 cycles. Polarization curve 1 is the polarization curve obtained from one activation cycle, while polarization curves 2 and 3 are the polarization curves obtained from the last two cycles. The voltage deviation between the seventh and sixth activation cycles was less than 10mV. The stack activation was completed. The total activation time was 210 minutes.

[0105] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. An activation method for a proton exchange membrane fuel cell stack based on an AC impedance meter, characterized in that, The specific steps are as follows: Step N1: Place the proton exchange membrane fuel cell on the test platform, connect the gas pipeline, and check the stack's airtightness. Step N2: Set the fuel cell temperature to 60℃. Introduce humidified nitrogen gas to the cathode and humidified hydrogen gas to the anode. Purge both the anode and cathode with nitrogen gas for 20 seconds. At this point, the humidity at both the anode and cathode is 100%. The gas pressure at both the anode and cathode is atmospheric pressure. The cathode flow rate is Flow Rate 1, and the cathode nitrogen purging flow rate 1 is 0.5 A / cm³, which is normal for the fuel cell stack. 2 The gas flow rate is: 0.01657 * 25 * 0.5 * 2.5 = 0.518 L / min. The anode flow rate is flow rate 2, and the anode hydrogen purging flow rate 2 is 0.5 A / cm³ during normal operation of the fuel cell stack. 2 The gas flow rate is: 0.00696 * 25 * 0.5 * 1.8 = 0.157 L / min; Step N3: The fuel cell stack temperature reaches 60°C and is maintained at 60°C for 5 minutes. The fuel cell stack pre-activation process is completed, and the fuel cell stack temperature is set to 70°C. Step N4: After the fuel cell stack temperature reaches 70℃ and stabilizes, stop supplying nitrogen to the cathode. Set the anode and cathode flow control to metering ratio mode and introduce humidified air. The minimum flow rate at the cathode is 0.518 L / min, the metering ratio is 2.5, the gas pressure is 90 kPa, and the humidity is 60%. The minimum flow rate at the anode is 0.157 L / min, the metering ratio is 1.8, the gas pressure is 100 kPa, and the humidity is 60%. Step N5, under-oxygen activation: Load the fuel cell stack to a voltage of 0.8V, then stop the air supply to the cathode. The stack voltage drops to 0.3V. Resume the air supply, disconnect the load, and the voltage returns to OCV. Repeat this step 5 times. Step N6, Constant Current Discharge Activation: Start applying 0.5V from OCV at a rate of 0.2 A / cm. 2 0.2 A / cm 2 Hold for 3-5 minutes, at a rate of 0.2 A / cm. 2 The value of the last selected point is used to form polarization curve 1; Step N7: Repeat steps N5 and N6 to obtain polarization curve 2. Use an AC impedance meter to measure the impedance value and determine whether the deviation of the average single-cell impedance of the two impedance curves is less than 0.2mΩ. The average single-cell impedance is equal to the total impedance value measured by the AC impedance meter / the number of single cells in the stack. If it is greater than 0.2mΩ, repeat steps N5, N6, and N7. If it is less than 0.2mΩ, proceed to step N8. Step N8: Determine whether the voltage deviation between polarization curve 2 and polarization curve 1 is less than 10mV under the same voltage of 0.4V and 0.6V and the same current. If so, the stack has been activated. If the voltage deviation between polarization curve 2 and polarization curve 1 is greater than or equal to 10mV, repeat step N8 until the voltage deviation between the new polarization curve and the previous polarization curve is less than 10mV, and the stack activation is complete.

2. The activation method for a proton exchange membrane fuel cell stack based on an AC impedance meter according to claim 1, characterized in that, Before step N1, there is also step N0, which checks whether the airtightness of the fuel cell stack meets the airtightness index. If it meets the airtightness index, proceed to step N1. If it does not meet the airtightness index, reassemble the fuel cell stack until the airtightness of the fuel cell stack meets the airtightness index.

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